Color-routers for image sensing

This case claims priority of U.S. Provisional Patent Application Ser. No. 63/108,622, filed Nov. 2, 2020, which is incorporated herein by reference. If there are any contradictions or inconsistencies in language between this application and one or more of the cases that have been incorporated by reference that might affect the interpretation of the claims in this case, the claims in this case should be interpreted to be consistent with the language in this case.

The present disclosure relates to image sensing in general, and, more particularly, to spectral and color management in image sensing applications.

High resolution image sensing technologies have exploded over the past decade. An important capability of all image sensors is to separate light into individual wavelength signals (each comprising a single wavelength component or multiple wavelength components) for detection by photodetectors located in corresponding pixels and/or sub-pixels. In most technologies today, this separation is done via absorbing color filters (e.g., blue, green, and red), which selectively transmit light in a desired wavelength band while absorbing all other light. Unfortunately, such filters have several significant drawbacks.

First, because optical energy outside the wavelength range of interest is absorbed, color filters intrinsically waste a significant amount of the light incident upon them—more than two-thirds in some cases.

Second, this absorption significantly reduces the total amount of light received at the pixel photodetectors, which degrades image-sensor performance.

Third, the amount of light incident on each an image-sensor pixel reduces quadratically with linear scaling of pixel size; therefore, the reduction in intensity of light at the photodetectors due to absorption by the color filters represents a bottleneck to scaling of pixel size for prior-art image sensors. This is particularly detrimental to the performance of pixels having sizes at or below the wavelength of the light they receive.

The need for a color-separation capability for image processors that enables small pixel size and/or high image-sensor performance remains, as yet, unmet in the prior-art.

An advance in the art is made according to aspects of the present disclosure which describes systems and apparatus for providing color selectivity in a substantially lossless manner (i.e., without significant absorption of incident light). Color-routers in accordance with the present disclosure selectively directly route virtually all photons of each given wavelength signal in a received light signal to only the photodetector of a plurality of photodetectors meant to receive that wavelength signal. This allows the use of smaller photodetectors because they collect more light than larger photodetectors coupled with color filters. As a result, image sensors in accordance with the present disclosure can be scaled to sizes heretofore unattainable by using photodetectors that are sub-wavelength in size.

An illustrative embodiment of the present disclosure is an image sensor comprising a plurality of pixel-repeat units, where each pixel-repeat unit includes a color-router disposed on a light-detection layer. The light-detection layer includes first, second, third, and fourth photodetectors, which are substantially identical and arranged in linear array. The color router covers these photodetectors, and is configured to receive light containing a plurality of wavelength signals and directly route each wavelength signal to a different photodetector. In the illustrative embodiment, each of four wavelength signals (each including a different one of blue, green, red, and near-infrared individual wavelength components) is directly routed to a different photodetector of a group of four photodetectors. The color-router is configured such that substantially all of the blue light incident on the pixel-repeat unit is selectively received at the first photodetector of the group, all of the green light incident on the pixel-repeat unit is selectively received at the second photodetector, all of the red light incident on the pixel-repeat unit is selectively received at the third photodetector, and all of the near-infrared light incident on the pixel-repeat unit is selectively received at the fourth photodetector. As a result, each pixel-repeat unit is able to provide spectrally selective detection with substantially perfect optical efficiency. Furthermore, because substantially all photons of each wavelength signal are directly routed to their respective photodetector, the color router additionally functions as both an anti-reflection layer and a lens element.

Each color router is a three-dimensional layer of substantially lossless silica containing an arrangement of nanoscale scatterers made of substantially lossless silicon nitride. The scatterers are configured such that their location, size, and shape enable each different wavelength signal in the received light to be completely directly routed to its corresponding photodetector. As a result, each photodetector receives substantially all of the optical energy of its respective wavelength signal and substantially none of the optical energy of the other wavelength signals.

In some embodiments, at least one of the substantially lossless medium and substantially lossless nanoscale scatterers comprises a different substantially lossless dielectric or other material, where the substantially lossless medium and substantially lossless nanoscale scatterers comprise materials having different dielectric constants.

In some embodiments, each of the light-detection layer and color router includes a different number of elements and/or the elements of each pixel-repeat unit are arranged in an arrangement other than that of a linear array, such as a 2×2 Bayer pattern, other two-dimensional arrangement (regular or irregular), and the like.

An embodiment in accordance with the present disclosure is an image-sensor pixel-repeat unit () for detecting each of a plurality of wavelength signals (B,G,R, andNIR) in a light signal () incident on the pixel-repeat unit, wherein the image-sensor pixel-repeat unit comprises: a light-detection layer () comprising a plurality of photodetectors (B,G,R, andNIR), the plurality of photodetectors being arranged in a first arrangement; and a color router () disposed on the light-detection layer, the color router comprising a first plurality of scatterers (), wherein the first plurality of scatterers is arranged within the color router in a second arrangement, and wherein the color router comprises a first material (M) having a first dielectric constant, and wherein each scatterer of the first plurality thereof comprising a second material (M) having a second dielectric constant that is different than the first dielectric constant; wherein the second arrangement is configured such that the plurality of wavelength signals is directly routed to the plurality of photodetectors such that each photodetector of the plurality thereof selectively receives a different wavelength signal of the plurality thereof.

Another embodiment in accordance with the present disclosure is a method for forming an image-sensor pixel-repeat unit () for detecting each of a plurality of wavelength signals (B,G,R, andNIR) in a light signal () incident on the pixel-repeat unit, wherein the method comprises: providing a light-detection layer () comprising a plurality of photodetectors (B,G,R, andNIR), the plurality of photodetectors being arranged in a first arrangement; and forming a color router () on the light-detection layer, the color router comprising a first plurality of scatterers () that is arranged within the color router in a second arrangement, and wherein the color router comprises a first material (M) having a first dielectric constant, and wherein each scatterer of the first plurality thereof comprising a second material (M) having a second dielectric constant that is different than the first dielectric constant; and defining the second arrangement such that the color router directly routes the plurality of wavelength signals to the plurality of photodetectors such that each photodetector of the plurality thereof selectively receives a different wavelength signal of the plurality thereof.

The following merely illustrates the principles of the disclosure. It will thus be appreciated that those skilled in the art will be able to devise various arrangements which, although not explicitly described or shown herein, embody the principles of the disclosure and are included within its spirit and scope.

Furthermore, all examples and conditional language recited herein are principally intended expressly to be only for pedagogical purposes to aid the reader in understanding the principles of the disclosure and the concepts contributed by the inventor(s) to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions.

Moreover, all statements herein reciting principles, aspects, and embodiments of the disclosure, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure.

Unless otherwise explicitly specified herein, the figures comprising the drawing are not drawn to scale.

The following terms are defined for use in the present Specification, including the appended claims:

depicts a schematic drawing of a cross-sectional view of an individual pixel-repeat unit of an illustrative embodiment of an image sensor in accordance with the present disclosure. Pixel-repeat unitincludes light-detection layerand color router, which is disposed directly on the light-detection layer. In some embodiments, a spacer layer is included between color routerand light detection layer. Pixel-repeat unitis a spectrally selective detection system configured to individually detect the wavelength signals included in light signal. In the depicted example, light signalcontains wavelength signalsR,G,B, andNIR, and pixel-repeat unitprovides output signals-through-, which are based on the intensity of wavelength signalsR,G,B, andNIR, respectively.

In the depicted example, each of wavelength signalsR,G,B, andNIR includes only one individual wavelength component. Specifically, wavelength signalB includes only blue light (i.e., a narrow spectral band centered at 450 nm), wavelength signalG includes only green light (i.e., a narrow spectral band centered at 550 nm), wavelength signalR includes only red light (i.e., a narrow spectral band centered at 650 nm), and wavelength signalNIR includes only near-infrared light (i.e., a narrow spectral band centered at 750 nm. In some embodiments, at least one wavelength signal routed by a color router includes more than one wavelength component.

Light-detection layer(hereinafter referred to as “LD layer”) includes photodetectors,G,R, andNIR, which are arranged in a linear array having uniform spacing or pitch Pand size W.

Photodetectors,G,R, andNIR (referred to, collectively, as photodetectors) are conventional photodetectors suitable for detecting light having any wavelength component within the spectral range of light signal.

In the depicted example, each of photodetectorshas a size Wof approximately 280 nm and pitch Pis approximately 400 nm. It should be noted that this photodetector pitch is approximately half the photodetector pitch of state-of-the-art image sensors that employ absorption color filters, which have a photodetector pitch of approximately 800 nm. In some embodiments, the spacing between photodetectors,G,R, andNIR is non-uniform. In some embodiments, pitch Pis less than or equal to the wavelength of the longest wavelength component included in light signal. In some embodiments, the size of photodetectors,G,R, andNIR is non-uniform. As will be apparent to one skilled in the art, after reading this Specification, the size, W, of photodetectorsand the spacing between them (i.e., pitch P) is a matter of design and any practical size and/or pitch can be used without departing from the scope of the present disclosure.

It should be noted that, although the depicted example operates over only a spectrum that visible and near-infrared light, embodiments in accordance with the present disclosure can be configured for operation at wavelengths within virtually any electromagnetic spectral range, such as infrared, ultraviolet, multiple spectral ranges, and the like.

Color routerhas a structure that includes a layer of background medium having thickness t, throughout which a three-dimensional arrangement of nanoscale scatterers is present. In the depicted example, thickness tis approximately 2 microns; however, color routercan have any practical thickness without departing from the scope of the present disclosure. Color routeris described in more detail below and with respect to-B. As discussed below, the material of the medium of color routerhas a first dielectric constant, while the material of the scatterers comprise a different material that has a second dielectric constant that is different (higher or lower) than the first dielectric constant. As will be apparent to one skilled in the art, the dielectric constant and refractive index of a material are related, where the dielectric constant εis the refractive index squared, ε=n.

Color routers in accordance with the present disclosure afford significant advantages over prior-art optical stack elements (which can include, e.g., lenses, absorptive color filters, cavity spectral filters, anti-reflection coatings, etc.) and prior-art color-separation elements (which can include, e.g., plasmonic color filters, plasmonic photon sorters, diffractive optical filters, color splitters, etc.), including:

Furthermore, it is an aspect of the present disclosure that the teachings herein enable a color router that directly routes the photons of a wavelength signal from the entry surface of the color router to their intended photodetector located at or within a wavelength of the exit surface of the color router. It should be noted that the direct-routing capability of color routers in accordance with the present disclosure is in direct contrast to meta-optics-based light-scattering structures, which rely on propagation of light over several wavelengths beyond the structures to focus and sort light spatially at the pixel photodetectors, such as those disclosed in U.S. Patent Publication No. 2020/0124866 or by P. Camayd-Munoz, et al., in “Multifunctional volumetric meta-optics for color and polarization image sensors,” in Optica, Vol. 7, pp. 280-282 (2020), each of which is incorporated herein by reference.

depicts operations of an exemplary method suitable for forming a color router in accordance with the present disclosure. Methodis described with continuing reference to, as well as reference to, which depict cross-sectional views of pixel-repeat unitat different stages of fabrication.

Methodbegins with operation, wherein a three-dimensional design for color routeris generated. In the depicted example, the design of color routeris realized via a computational approach that aims for systematic optimization of an objective function. This objective function can be related to the photon efficiency with which the light incident on the color router is separated and redirected to different photodetectors depending on its spectral content (color).

depicts sub-operations of a non-limiting example of a sub-method suitable for designing a color router in accordance with the present disclosure. Operationbegins with sub-operation, wherein a candidate design for color routeris established.

At sub-operation, the candidate design for color routeris simulated using an electromagnetic simulation. Examples of electromagnetic simulations suitable for use in accordance with the present disclosure include, without limitation, finite-difference time-domain, finite-difference frequency-domain, finite element, and the like.

At sub-operation, for the proposed color-router-structure design, an adjoint variable method is used to estimate the gradient of the objective function with respect to a plurality of design parameters. Preferably, this adjoint variable method includes at least two full electromagnetic simulations of the structure.

At sub-operation, the structure of the color router is updated along the direction of the gradient. It should be noted that any or all degrees of freedom in the color-router structure can be adjusted in parallel. Degrees of freedom are adjusted to respect bound constraints of the material dielectrics available for use in design region.

At sub-operation, this performance of the given color-router structure is evaluated against a set of performance metrics. Typically, these metrics primarily include routing efficiency into the desired channel, which, preferably, should be maximized while also measuring reflection and cross talk to attempt to minimize them. If the performance is deemed less than satisfactory, sub-methodreturns to sub-operation. Note that sub-operationsthroughcan be iterated as many times as necessary to realize a color router design that is satisfactory.

If the performance satisfies the design criteria, however, sub-methodcontinues with sub sub-operation, in which a scatterer-pattern-is established for each of sub-layers-through-N, where each scatterer pattern includes a two-dimensional arrangement of scatterers that is based upon the position of its respective sub-layer within the arrangement of the N sub-layers along the z-direction.

The value of N depends on the desired performance for the color router, among other factors. Typically, has a value within the range of approximately 5 to approximately 40; however, any practical number of sub-layers, from just one layer to a few sub-layers to many dozen sub-layers or more, can be used in a color router without departing from the scope of the present disclosure.

It should be noted that, in some embodiments, the number, N, of sub-layers is established as part of sub-operation.

Returning now to method, for each of i=1 through N:

At operation, media layer-is formed. Media layer-comprises material M, which has a first dielectric constant ε=1. In the depicted example, material Mis silica having a dielectric constant of approximately 2.1. It should be noted that, preferably, photodetectorsare passivated by encasing them in dielectric material. In the depicted example, photodetectorsare encased in material M, which also forms spacer layer. As a result, media layer-is formed on space layer.

At operation, a two-dimensional void pattern-of voidsis formed in media layer-. The arrangement of void pattern-corresponds to the position of sub-layer-within the arrangement of the N sub-layers of color router, as determined in sub-operation, as discussed above. In the depicted example, voidsare approximately 10 nm by 10 nm in size (i.e., the design-element size is 10 nm by 10 nm), with abutting individual voids collectively defining larger features. It should be noted, however, that any suitable dimension for voidscan be used without departing from the scope of the present disclosure.

shows a cross-sectional view of nascent pixel-repeat unit′ after formation of void pattern-.

At operation, voidsare filled with material M, which has a second dielectric constant, ε=2, to form scatterers, which have substantially the same dimensions as voids. Within each of layers-, scatterersare arranged in scatterer pattern-, which matches void pattern-. In the depicted example, material Mis silicon nitride having a dielectric constant of approximately 4.0.

shows a cross-sectional view of nascent pixel-repeat unit′ after formation of scatterer pattern-in media layer-.

Once voidsA contain material M, media layer-and scatterer patternA-collectively define sub-layer-

It should be noted that any of a wide range of suitable materials can be used for the materials included in color router. However, embodiments in accordance with the present disclosure derive significant advantages over the prior art by using lossless dielectric materials for the materials of color router. For example, the use of lossless materials enables all of the light incident on each pixel-repeat unit to be collected, while each wavelength signal is directly routed to a corresponding photodetector with nearly perfect optical efficiency. As a result, substantially lossless dielectric materials, such as silica, silicon oxides, silicon nitrides, silicon oxynitrides, titanium dioxide, hafnium oxide and the like, are typically preferred for operation in the visible spectrum. As will be apparent to one skilled in the art, after reading this Specification, the loss of a material is dependent upon the wavelength of operation; therefore, different dielectric materials, such as silicon, germanium, gallium phosphide, magnesium fluoride, zinc selenide, zinc sulfide, barium fluoride, calcium fluoride, sapphire, amorphous silicon dioxide are preferable for color routers designed for operation in other wavelength ranges, such as the ultraviolet wavelength range, mid-infrared wavelength range, long-infrared wavelength range, and the like.

At optional operation, sub-layer-is planarized.

Operationsthroughare repeated N times such that sub-layers-through-N collectively define color routerand scatterer patterns-through-N collectively define three-dimensional scatterer arrangement.

shows a cross-sectional view of pixel-repeat unitafter completion of sub-layer-N and, therefore, color router.

In the depicted example, color routeral of scattererscomprise the same material. However, in some embodiments, scatterers in color routerare made of more than one material.